Impact of clays on CO2 adsorption and enhanced gas recovery in sandstone reservoirs

Abstract

Carbon dioxide enhanced gas recovery (EGR) is a promising technique to sequester CO2 and boost natural gas recovery from conventional depleted and unconventional tight gas reservoirs. Clay minerals are usually present in sandstone reservoirs and their influence on the efficiency of CO2-EGR is yet to be examined. In this study, the impact of clays on CO2 adsorption was evaluated for different sandstone rocks with various amounts and types of clays in the temperature range from 50–100 °C and pressures up 20 bars. The results showed that the adsorption of CO2 on sandstone rocks depends on the clay type, amount, and distribution. Clay-rich sandstone rocks, which have swellable clays such as illite, showed the highest CO2 uptake at a temperature of 50 °C and a pressure of 20 bars with total CO2 uptake of 4.6 and 2.6 mg/g for Kentucky and Scioto rocks, respectively. In contrast, sandstone samples with low clay content and a considerable percentage of carbonates showed CO2 uptake just above 1.5 mg/g for Bandera sandstone and 1.1 mg/ gm for Berea sandstone at similar conditions. Moreover, raising the temperature to 75 °C decreased the CO2 uptake on sandstones. However, the alteration of clays crystallinity at a temperature of 100 °C improves the CO2 adsorption. Adsorption isotherm analysis revealed that at the CO2 adsorption is monolayer at low temperature (50 °C) and pressure of 20 bars; whereas multilayer adsorption at 75 and 100 °C is predicted by Freundlich isotherm model. The thermodynamic analysis illustrated that the adsorption of CO2 on sandstone rocks is physisorption and exothermic on Kentucky, Scioto, and Berea sandstones and endothermic on Bandera sandstone. Core flooding experiments at 100 °C revealed the potential of CO2-EGR for clay-rich sandstone and highlighted the role of clays distribution.